Machine tools generally manipulate a workpiece by actuating and/or biasing tool components in many different directions. For example, one machine tool is a machining center with a removable generating head. As discussed below and in light of this machining center example, each component of motion effected by the machine tool is herein called an "axis."
The generating head can rotate in a rotational direction about its center line so that its blade removes material from a workpiece by physical interference. The rotational position is considered to be one axis of the tool, herein called the rotational axis. Of course, the rotational position of the head is related to the rotational velocity and acceleration, and these quantities are also considered to be part of the rotational axis. Generally speaking, the rotational component of motion effected by the machining center tool is the rotational axis.
The machining center can also actuate the generating head along the longitudinal direction of its centerline, in order to move further in or out of the body of the workpiece. This longitudinal motion is considered to be a second axis of the tool, herein called the longitudinal axis.
In some machining centers, the workpiece can be moved in one or more directions relative to the generating head. The motion (e.g., position acceleration, etc.) of the workpiece in these directions would be additional axes of the machining center tool. Now that the concept of an "axis" has been explained, the use of a "fluid axis" will be discussed below.
In some conventional tools, pressurized fluid can be utilized to help cool, position or provide a biasing force on the operative parts of the tool. For example, U.S. Pat. No. 5,775,853 discloses a squirt reamer wherein hydraulics control the longitudinal position of the squirt reamer head.
As another example, U.S. Pat. No. 4,913,602 to Peter et al. discloses a boring head for treating or cutting of hollow cylinder surfaces with a cutting edge that is radially adjustable by means of hydraulic pressure. The hydraulic pressure, and the radial adjustment effected thereby, can be considered to be the fluid axis of this boring head tool.
As used herein, the term reference information means any information used in controlling a tool axis. Feedback, which is derived from the controlled axis itself, is one kind of reference information. Conventionally, some tools control a fluid axis based upon feedback reference information to effect closed loop servo control of the fluid axis (e.g., fluid pressure). However, the feedback reference information employed in this closed loop servo control is generally limited to the fluid pressure itself. Of course, feedback reference information based on the actual fluid pressure can be usefully employed to control the fluid pressure to maintain some constant, predetermined pressure value.
However, fine adjustments and continuous adjustments to the fluid axis can not be made based on the other axis of the tool, because the values (e.g., positions, velocities, etc.) related to the other axes of the tool are not employed as reference information in control of the fluid axis.
It is advantageous to use only fluid axis feedback information to effect closed loop servo control of a fluid axis. This kind of control requires relatively infrequent binary signals to be sent between the computerized numeric control (CNC), which controls the electromechanical components of the tool, and the fluid regulation hardware (e.g., a valve). For example, a low speed serial interface can be used between a CNC and fluid regulation hardware.